1. Field of the Invention
The present invention relates to a differential limiting control apparatus for a vehicle installed between a front axle and a rear axle of a four wheel drive vehicle, particularly to a differential limiting a differential motion between rotational shafts of front and rear wheel.
2. Description of the Related Art
Conventionally, as a differential limiting control between one rotational shaft and the other rotational shaft, in particular, between front and rear axles of a four wheel drive vehicle, a technique has been known in which an actual differential speed between the rotational shafts is detected is caused to converge to a target differential speed by a feedback control through a PID (proportional Integration and Differentiation) control.
Under various kinetic conditions of the vehicle, however, there may be caused a risk that a simple PID control causes response and hunting problems, and to cope with this, a countermeasure is adopted in which respective gains in the PID control are interlocked with other parameters (such as lateral acceleration, acceleration, yaw rate). For example, JP-A-6-211063 discloses a technique in which a proportional term gain, a differential term gain and an integral term gain are variably set in accordance with a speed differential between one rotating shaft and another rotating shaft when a yawing momentum is feedback controlled through a PD control or PID control by distributing the driving force between left and right wheels or front and rear wheels.
In the technique in which the aforesaid gains are interlocked with the other parameters to be set, however, to deal with the respective parameters which change every moment while the vehicle is running, highly accurate sensors and high-speed computation processing functions are required. However, when attempting to realize a highly accurate and good-response traction performance, there are caused problems that the costs of a whole system are increased and that the system becomes complicated.